12 BULLETIN 210, U. S. DEPARTMENT OE AGRICULTURE. 



Table 5. — Distribution of the seed crop of western white pine, by crown classes. 



Ratios of seed production of crown classes. 1 



Class I. Class II. Class III. Class IV. Class V. Total. 



Plot No. 1. 



Total yield per cent 



Number of trees do. . 



Plot No. 0. 



Total yield do . . 



Number of trees do. . 



Plot No. S. 



Total yield do. . 



Number of trees do. . 



Plot No. 4. 



Total yield do. . 



Number of trees do. . 



Average 



59.1 

 30 



59.5 

 15 



30.9 

 10 



49.3 



39.7 

 30 



37.6 

 20 



66.0 

 23 



50.5 

 37 



L2 

 12 



2J9 



15 



hi 



18 



02 

 34 



100 

 100 



100 

 100 



100 

 100 



100 

 100 



54.3 

 15 



44.5 

 27 



hi 

 21 



100 

 100 



1 Expressed in percentage of seed produced in each crown class of the plot divided by percentage of trees 

 in the crown class. 



The ratios of productivity of trees of different crown classes in 

 round figures are 3.5, 1.5, 0.05, 0.0. Thus a tree of crown Class I 

 bears 70 times and a tree of crown Class II 30 times more seed than 

 a tree of Class III. 



The participation of the different crown classes in the production 

 of seed may serve as an index of the seed crop. In exceptionally 

 good seed years not only the dominant classes bear seed, but even 

 the oppressed trees have occasional cones, while in poor seed years 

 cones are to be found only in the dominant class (I), and even then 

 not on all trees or parts of their crowns. Between these two ex- 

 tremes range seed crops of various abundance. The abundance 

 of the seed crop can, therefore, be prognosticated very early in the 

 summer by observing in the forest the kind of trees that bear cones. 

 In order to establish a regular yield for the seed production of western 

 white pine, it would be necessary accurately to measure the crop 

 by the method described over several .seed years of various intensity. 

 After the seed production for the poorest, moderate, and excep- 

 tionally good seed years is ascertained, the determination of whether 

 the crop of a given year is good, fair, or poor can then be forecasted 

 easily and early by merely observing the different crown classes of 

 trees that are bearing cones. 



An attempt to penetrate deeper into the causes that determine 

 the average amount of seed produced by an individual tree of each 

 crown class meets with difficulties because of the many counteracting 

 factors, some of which still remain unexplained. Aside from the 



